Various types and shapes of boat hulls are known in the industry. Many boat hulls are specifically designed for planing when operating above a certain speed. To help achieve better high speed planing performance, many boat hulls are provided with a stepped aft portion which allows raising the motor lower unit and propeller relative to the planing surface of the boat bottom and effectively moves the longitudinal center of gravity closer to the aft edge of the planing surface. The step provides an elevated surface portion at the aft end of the boat hull which may be provided with a different contour than the planing surface immediately forward of the stepped portion of the boat hull. While such boat hull designs are effective to help achieve higher speed planning performance, they present some low speed problems.
As suggested above, performance boat hulls that are built to run with outboard engines typically have a transom structure that are designed to handle the power and weight of the outboard motor that is specified for it. Those transoms usually have some sort of reinforcement supporting them that transfers some of the loads from the static and dynamic forces imposed on them to other structural parts of the hull such as stringers and ultimately, to larger areas of the hull skin and or deck structures. The common practice is to install the transom as one operation and component and then follow with the installation of the reinforcing members as another operation and separate components. These reinforcements are often referred to as “knees, braces, gussets, etc.”. Often this arrangement is in unison with a step or pocket designed in the hull at the aft end of the planing surface that allows the engine to be mounted higher to reduce drag and effectively moves the propeller aft of the trailing edge of the planning surface, thereby creating a torque that will raise the bow of the boat when under power without excessive trim being applied to the engine. This type of pocket or step makes the transom structure more complex and often creates an area that develops a vacuum or drag at low speeds and impairs the hull's ability to get on plane.
One problem with such a stepped boat hull transom area is the formation of a suction or vacuum that produces drag on the boat during the transition to true planing speeds. To help alleviate this drag problem, various venting systems have been provided that allow air to be fed from the atmosphere to the region of the transom step which has been found to reduce the suction and decrease the drag on the boat during low speed operation. The step also allows raising the propeller relative to the boat bottom which reduces a bow lifting torque induced by the thrust of the propeller and the drag component of the portion of the motor lower unit that is in the water.
One means of providing a vent to the step area on the boat hull bottom was to provide a riser tube in the boat that simply allowed air to be fed to the exterior region of step with the amount of air flow being determined by the level of suction. The higher the suction, the more air drawn and vice versa. While this was effective in reducing suction, it did have problems. When the vent tube was inside of the boat, often times, water would be fed upwardly through the vent tube and into the boat. This was a particular problem during reversing of the direction of the prop thrust for example by putting the motor in reverse. Examples of such a venting system in a watercraft can be found in U.S. Pat. Nos. 6,412,434, 4,689,026 and 4,231,314.
Another venting system can be found in U.S. Pat. No. 5,111,767. In this patent, a boat hull is formed and a separate flow channel forming member is added to the boat hull after the boat hull is formed. It is generally triangularly shaped having two opposing panels defining a channel therebetween. A pair of the side edges defining the member have outwardly extending flanges which are secured to the inside surface of the boat one set of flanges being secured to the transom and one set of flanges being secured to a riser in the boat at the location of the step on the outside of the boat hull. Holes are then drilled through the transom and the riser to provide fluid flow communication of the flow channel in the member and the atmosphere and the region under the boat in the step area. Fluid flow can then be accomplished between the vent holes via the flow channel in the attached member. Water could become trapped within the flow channel in the member and a drain hole is provided. However, keeping the drain hole and the vent holes clean can be problematic and air cannot flow to the step recess until the water in the passage has been evacuated. The evacuation process, if prolonged, can hinder initial planing performance. The member in combination with the transom and boat bottom, formed a closed chamber until holes were formed. Forming the openings requires precise locations of the holes to prevent the formation of a leakage area into the interior of the boat hull and additional manufacturing steps.
There is thus a need for an improved vented boat hull.